Propeller blade attachment



Jan. 4, 1949. I G EEN 2,457,815

PROPELLER BLADE ATTACHMENT Filed Aug. 2, 1944 an a FIG. 3

- IN VEN TOR.

Navel/ 1v 6 Gees/v Patented Jan. 4, 1949 2,457,815 a PROPELLER BLADEATTACHMENT Marvin C. Green, Dayton, Ohio 5 H Application August 2, 1944,serial at; 847,762

11 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described hereinmay be manufactured and used by or for Government for governmentalpurposes, without the payment to me of any royalty thereon.

This invention relates to means for attaching non-ferrous propellerbaldes to hubs and constitutes an improvement over related subjectmatter disclosed in the copending application Serial No. 483,006, filedApril 14, 1943, of C. R. Gaskell and M. C. Green now Patent 2,368,656dated Feb. 6, 1945.

closed for attaching propeller blades to hubs, comprising a hub memberand a plurality of symmetrically arranged screws disposed parallel tothe axis of a propeller blade. having a shank adapted to be inserted bya force fit into a ferrule on the hub member. A compression plate issecured within the hub member, through which the screws pass, the screwshaving heads abutting the plate and threaded ends adapted to be screwedinto the blade shank. This construction, theoretically, provides theblade with support against bending stress by virtue of the force fitbetween the blade shank and the ferrule, while radial stresses in theblade due to centrifugal force are resisted by tensile stresses in thescrews which are transmitted to the compression plate by reason of theabutment of the screw heads thereon. As a matter of actual practice,however, it is desirable to protect the screws against contingencieswherein some bending stresses may be transmitted thereto which wouldcause certain screws to be stressed more than others and my presentinvention has for an object the provision of means for substantiallyequalizing tensile stresses among the several screws ofthe structure.Further, it has been found in practice that In the copendingapplication, devices are dissubjected successively to the sametightening torque, rather wide deviations in tensile stress among theseveral screws occur, caused by differences in tensile reaction in theshank material as the shank is being drawn into the ferrule, this beingespecially true of wooden blades. Accordingly, it is another object ofmy invention to provide a propeller blade attaching structure asdisclosed in the copending application with means for distributing andequalizing initial tensioning stresses among the several screws, and itis a further object to provide a simple, rugged and compact structurefor accomplishing these ends.

In accordance with the objects of the invention, I provide propellerblade attachment means substantially as disclosed in the copendingapplication but having additional structure comprising an elasticmaterial, such as rubber, confined between a pair of compression platesand so disposed that compression stresses are transmitted thereto inreaction to the tensile stresses in the screws. Due to the comparativeincompressibility of a confined elastic material, a reaction resultssimilar to that of a liquid under pressure, in that the pressure isequally distributed throughout the material. In this manner, increasingor decreasing tensile stresses in one or more screws reacts on theelastic material correspondingly whereby such deviations are distributedsubstantially equally among the several screws by an arrangementdisclosed in detail with reference to the appended drawings. in which:

Fig. 1 shows a longitudinal section of a preferred form of the device;

Fig 2 shows a modification thereof;

Fig. 3 illustrates a further modification; and

Fig. 4 shows a fragmentary perspective of a modification of certainelements of Fig. 3.

In Fig. 1, a propeller hub member A is shown having a threaded end I forengagement with a hub (not shown) and having a ferruled end 2 in whichis force fitted the circular shank 3 of a propeller blade. Shank 3 has achamfered end 4 engaging a beveled shoulder 5 at the base of the ferrule2. Engagement of chamfered surfaces 4 and 5 tends to center shank 3 inaxial alignment with-ferrule 2 and also tends to relieve longitudinalshear stresses in shank 3 due to the tensile loading thereof. Fourscrews 1, 8, 9, iii are shown as representative of a plurality of screwsarranged in symmetrical configurations, e. g., screws 1 and Ill lie on acircle disposed about the axis of shank 3 and screws 8 and 9 lie on asmaller concentric circle. Screws 1 through. ID are in. threadedengagement with shank 3 and extend toward the hub through a compressionplate ll. Plate H is disposed within hub Aand has a sloping shoulder i2engaging sloping shoulder I: of the hub. The purpose of the slopingengagement of shoulders I! and I3 is to provide a force componentagainst shoulder l2 tending to counteract buckling of plate ll upwardlyat the center due to tensile stress in screws 1 through l0. Plate II hasa recess l5 containing an elastic material [6, such as rubber, or thelike, confined by means of a second compression plate l8 disposedcontiguous thereto. The screws I through Ill pass through alignedperforations in elastic material It and the plate l8 and terminate inheads 20 through 23, respectively, abutting the exterior surface of theplate Hi. When tensile stresses are introducedinto the screws 1 throughill, the respective abutting heads 20 through 23 exert a force on plate18 tending to compress elastic material l6 within the recess IS. Theplate i3 has a smooth peripheral fit with recess l5 and is sufficientlythick to provide rigidity so that a tilting action thereof is obtainablein the event of the introduction of an unequal distribution of stressesamong the screws. Consider, for example, that screw 1 has a tensilestress introduced therein greater than that of screw Hi. The increasedstress will be trans-' mitted through screw head 20 and tend to drawplate l8 into the elastic material l6, thus causing a compressive stressin the material locally surrounding screw 1. Due to the comparativeincompressibility of the confined elastic material, elastic fiow thereinwill take place forcing or squeezing displaced material toward screw IIIwhereby the portion of plate 18 adjacent thereto will be forcedoutwardly, increasing the tensile stress in screw ID by virtue of theabutment of plate ill with screw head 23. The tilting action thusproduced is, however, very minute so that no extrusion of the elasticmaterial is at its peripheral engagement with recess i5 is experiencedto any degrees affecting operation of the device. In this mannerequalization of tensile stresses among the several screws is obtained asa matter of actual practice, and it has been found that for a propellershank approximately four inches in diameter operative thicknesses of theelastic material l6 and plate l8 of about oneeighth of an inch eachproduces satisfactory results. In addition to the tilting action ofplate iii a further effect has been observed in that plate I8 is subjectunder conditions of heavy stress to local flexing in areas underneathheavily stressed screw heads. When one or more screws receive increasedtensile stress suificient to pull the locally surrounding area of platel8 into the elastic material l6, elastic flow within the material takesplace, causing a displacement of material against unstressed areas ofplate l8 which distributes the increased tensile stress against theheads of the lesser strained screws. The fiexing action thus tendstoward distribution of substantially equal stresses among the severalscrews. It will, of course, be understood that local fiexing of plate l3should be within the elastic limit thereof, a consideration which is amatter of design and depends primarily upon the number of screwsintended to be used and the stresses expected to be encountered as wellas on the stress-strain characteristics of plate l8.

Referring to Fig. 2, a device similar to that disclosed in Fig. l isshown, the chief distinction residing in the coaction of the compressionplate 25 and the hub member 26 with a sealing gasket 21 interposedtherebetween, for the purpose of sealing wooden blade shanks againstmoisture changes. The compression plate 25 is provided with threads 28for engagement in a propeller hub. I

The modification shown in Fig. 3 comprises two hub members 30 and 3|, ashank 32 of a propeller plate being secured against bending stresses bya force fit within hub member 30. A compression plate 33 is securedwithin hub member 3| by a plurality of screws 35 and has a recess 36wherein is confined an elastic material 3'l. A plurality of screws 40through 44 pass individually through a corresponding plurality ofcompression plates 45 through 49, respectively, and have threadedengagement with shank 32 at one end and screw heads 5| through 55 inabutting engagement with plates 45 through 49, respectively, at theirother ends. To simplify illustration of this structure, Fig. 3 showsindividual compression plates 45 through 49, cooperating respectivelywith screws 40 through 44, but it will be understood by reference toFig. 4 that the allocation of screws to compression plates is a matterof design. The area of the elastic material covered by individualcompression plates is likewise a matter of desi n, as is the shape ofsuch plates.

In Fig. 4, for example, five compression plates Ell through 64 are showncontiguous with elastic material 6-5 and provided with apertures 66 toaccommodate 5 screws per plate. By confining an elastic material with aplurality of relatively reciprocal compression plates as shown in Figs.3 and'4, the need for critical design of a single plate member such asthe plate IS in the form shown in Fig. 1 is eliminated. Each individualplate may be considered as a separate piston exerting compressive stressagainst the local area of the elastic material with which it iscontiguous. As heretofore described, since the elastic material acts asa liquid and transmits pressure stresses equally in all directions, itmay be seen that if any stress tends to force one plate, as plate 45 ofFig. 3, into the elastic material 31, a distribution of stress willoccur therein, acting outwardly against plates 46 through 49, therebytending to equalize stresses among the several screws 40 through 44.

Although I have shown in the modifications herein disclosed, relativelysimple configurations of screws for securing a propeller shank to a hubmember, it will be understood that the configuration used in practice isa matter of design, and as a matter of actual practice it has been foundthat configurations more complicated than those disclosed herein operatesatisfactorily in accordance with the principles set forth.

Having now described the invention and preferred form of embodimentthereof it is to be understood that the said invention is to be limited,not to the specific details herein set forth but only by the scope ofthe claims which follow.

I claim:

1. In a propeller mount, a propeller blade having a shank, a hub memberhaving ferrule means receiving the shank of said propeller blade, andmeans for securing the propeller blade shank to said hub membercomprising a plate member associated in fixed relation with said hubmember and having a recess in one face thereof opposite the hub memberferrule means, compression plate means slidingly disposed in andcompletely covering said recess and capable of tilting action, anelastic material confined within and completely filling said recessbetween said compression plate means and the walls of said recess andadapted to flow in the manner of an incompressible liquid, and aplurality of tension members bearing on the compression plate means witha portion passing through the compression plate means, elastic materialand plate member and secured to said propeller blade shank and operativeto compressively stress said elastic material between said compressionplate means and said plate member when said tension members aretensilely stressed.

2. In a mount for a propeller blade, a propeller blade having a shank, ahub means adapted to receive the shank of said propeller blade, meanssecuring said propeller blade shank to said hub I means comprising, atransverse wall ai'iixedly as.- sociated within said hub means, acompression plate means in interiltting relation with said transversewall on a side opposite the propeller shank receiving end of said hubmeans and capable of tilting action, said interfltting relation of saidtransverse wall and said compression plate means forming a completelyenclosed chamber, a resilient material confined by and completelyfilling said chamber and adapted to flow in a manner of anincompressible liquid, and tension members secured to said propellerblade shank passing through said transverse wall, resilient material andcompression plate means and bearing on the side of said compressionplate means opposite said resilient material whereby the total tensilestress exerted on said propeller shank is compressively transmittedthrough said resilient material and is distributed between said tensionmembers by elastic flow in said resilient material.

3. In a mount for a propeller blade, a propeller blade having a shank, ahub member having ferrule means receiving and radially securing theshank of said propeller blade, a transversely disposed wall in said hubmember with a recess on a side thereof opposite said ferrule means, acompression member slidingly fitting in said recess to form a completelyclosed chamber, an elastic material completely filling said chamber andadapted to flow in the manner of an incompressible liquid within saidchamber, tension members disposed to exert tensile stresses between saidpropeller shank and said compression member'and thereby compressivelystressing said elastic material, said tension members extending axiallyparallel to said propeller shank and through, respectively, saidcompression plate, said elastic material and said transversely disposedwall, whereby elastic flow in said elastic material is operative todistribute changes in tensile stress in one or more of said tensilemembers substantially equally between substantially all of said tensionmembers by reacting against said compression plate.

t. In a. mount for a propeller blade, a propeller blade having a shank,a hub member having ferrule means receiving the shank of said propellerblade, means for providing a recess within said hub member-comprising atransversely disposed plate retained therein forming a wall of saidrecess between the blade shank and said recess, an elastic materialsubstantially confined within and completely filling said recess,compression means completely covering said elastic material on the sidethereof opposite said wall to differentially stress said elasticmaterial in compression at a plurality of areas thereon, tension membersconnected to said blade shank and disposed to exert tensile stressbetween said propeller shank and said compression means forcompressively stressing said elastic material at said plurality ofareas, whereby elastic displacement in said elastic ma terial isoperative to distribute the total tensile stress between said tensionmembers substantially equally therebetween.

5. In a propeller mount, a propeller blade having a shank, hub means,means for securing the shank of said propeller blade in said hub meanscomprising a transverse plate provided with a recessed face retained insaid hub means with said recessed face opposite said blade shank, anelastic material adapted to flow in the manner of an incompressibleliquid retained within and completely filling said recess, a compressionplate local stresses contiguous with a surface of said elastic materialand completely covering said recess to substantially confine saidelastic material within said recess, a plurality of tension membersassociated. with said blade shank and adapted to individually exerttensile stress between the shank of said propeller blade and saidcompression plate for compressively stressing said elastic material,thereby distributing the total stress substantially equally among saidplurality of tension members by elastic flow displacement within saidelastic material.

6. In a propeller mount, a propeller blade having a shank, hub means,means for securing the shank of said propeller blade to said hub meanscomprising a transverse wall provided with an annular recess retained insaid hub means with said annular recess opposite said shank, an elasticmaterial substantially filling said recess and confined therein by acompression plate contiguous with a surface of said elastic material andadapted to be slightly tilted relative said transverse wall, a pluralityof tension members for exerting stress between said propeller bladeshank and said compression plate and operative to tilt said compressionplate upon a condition of unequal stress among said tension memberswhereby elastic flow displacement in said elastic material is operativeto equalize tensile stresses among said tension members.

'7. In a mount for attaching a propeller blade to a hub, a propellerblade having a shank, a hub member having means for securing the shankof said propeller blade therein comprising a removable' platetransversely disposed relative to the axis of saidshank in said hubmeans, a recess in the. face of said plate opposite said shank, anelastic material adapted to flow in the manner of an incompressibleliquid completely filling said recess, a disk-like compression plate ofa thick ness to allow local flexing under heavy local stress with headsabutting the opposite face of said compression plate so that tensilestresses in said tension members compressively stress said elasticmaterial whereby unequal stresses among said tension members areoperative by elastic flow displacement within said elastic material todifferentially flex areas of said compression plate thereby increasingthe tensile stress in thelesser stressed tension members for the purposeof distributing the total tensile stress between the shank of saidpropeller blade and said compression plate substantially equally amongthe plurality of tension members.

8. In a mount for attaching a propeller blade to a hub, a pr pellerblade having a shank, a hub member having means for securing the shankof said propeller blade therein comprising a removable platetransversely disposed relative to the axis of said shank in said hubmember, a recess in the face ofsaid plate opposite said shank, anelastic material having the elastic characteristics of an incompressibleliquid completely filling said recess, a disk-like compression plate ofa thickness to permit local flexing under heavy stress slidably disposedwithin and completely covering said recess to substantially confine saidelastic material therein and contiguous therewith, a pl rality ofelongated tension members extending through suitably alignedperforations in said canpresslon plate, said elastic material and saidtransversely disposed plate, respectively, and having ends adapted to besecured within said shank of said propeller blade, opposite ends of sadtension members being provided with heads abutting said compressionplate so that tensile stresses in said tension members compressivelystress said elastic material whereby unequal stresses among said tensionmembers are operative by elastic flow displacement within said elasticmaterial to diiferentially react on areas of said compression platethereby increasing the tensile stress in the lesser stressed tensionmembers for the purpose of distributing the total tensile stress betweenthe shank of said propeller blade and said compression platesubstantially equally among the plurality of tension members.

9. In a mount for a propeller blade, a propeller blade having a shank, ahub member comprising ferrule means for securing the shank of saidpropeller blade, a transverse wall within said hub membena recess withina face of said wall opposite said blade shank, an elastic materialsubstantially filling said recess, a plurality of compression platescontiguous with the surface of said elastic material and substantiallyconfining said elastic material within said recess and a plurality oftension members equally apportioned among said several compressionplates and having abutting engagement with the external surfaces oftheir respective plates and having shank portions extending throughsuitably aligned perforations in said compression plates, said elasticmaterial and said transverse wall, respectively, for threaded engagementwith the shank of said propeller blade whereby unequal tensile stressesamong said tension members is operative to differentially, compressivelystress areas of said elastic material and cause elastic flowdisplacement therein reacting against said compression plates for thepurpose of equalizing tensile stresses among the plurality of tensionmembers.

10. In a propeller blade retention means of the character wherein thepropeller blade shank is socketed in a hub member adapted to transmitloads on the blade to a propeller hub, and having tension screws securedin the blade shank parallel to the blade axis for transmitting tensionloads from the blade shank to the hub member, the improvement whichcomprises providing a transverse wall member within said hub memberarranged below the propeller blade shank and screws.

secured to the hub member, said wall member containing apertures for thepassage of the tension screws therethrough, a cylindrical recess in saidwall member on the side more removed from the propeller shank, aresilient rubber-like material adapted to flow in the manner of anincompressible liquid within and completely filling said recess, andcompression plate means of a thickness to permit local flexing underheavy local stress completely covering said cylindrical recess engagedby said tension screws and in compressive contact with said resilientmaterial, and plastic flow in the resilient rubber-like materialproviding for substantial equalization of the tension loads in thescrews.

11. Improvement in non-ferrous propeller blade retention meanscomprising a hollow sleeve member adapted to be received in a propellerhub structure, a propeller blade having a cylindrical shank portion,said cylindrical shank portion on the propeller blade socketed withinsaid sleeve, a plurality of radially extending tension screws withinsaid sleeve member and threaded into said blade shank parallel with theshank axis, a transverse wall secured within said sleeve member radiallyinward thereof from the end of the blade shank, said wall member beingapertured for free sliding passage of said screws therethrough,transverse abutment means positioned within said sleeve for movementwith respect to said transverse wall, said screws' having loadtransmitting engagement with the abutment means, said wall and abutmentmeans cooperating to define a chamber therebetween and a rubber-likematerial completely filling said chamber and resisting any change involume thereof, thereby transmitting loads to the wall member andequalizing loads transmitted from the respective MARVIN C. GREEN.

REFERENCES CITED I The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,727,609 Kramer Sept. 10, 19292,051,205- Estabrook Aug, 18, 1936 2,254,821 Haw Sept. 2, 1931 2,270,583Forton Jan. 20, 1942 2,339,549 Kubaugh Jan, 18, 1944 2,368,656 GaskellFeb. 6, 1945 FOREIGN PATENTS Number Country Date 508,146 Great BritainJune 27, 1939

